HoB4 at high pressure and low temperature: an experimental and theoretical study

Single crystals of HoB4 have been grown and used for synchrotron X-ray diffraction studies at pressures up to 23GPa and temperatures down to 100K. The experimental bulk modulus 195 +/- 6GPa is in good agreement with 188.4 and 198.2GPa values calculated in the LSDA and LSDA+U approximations, indicating that mainly the boron sublattice determines the bulk modulus. The experimental c/a ratio decreases slightly with pressure, but the effect is small. An orthorhombic distortion begins at Tc approximate to 295K, i.e. at a temperature much higher than the Neel temperature TN1=7.1K. The behavior is interpreted in terms of built-in strains and crystal mosaicity.